MAPT and frontotemporal dementia: To initially validate the antibodies that we used for tau imaging, we employed a HEK293 cell line that stably expresses the 0N4R isoform of human tau, bearing the frontotemporal dementia-associated mutation P301S, with a C-terminal Venus tag.15 We aimed to induce the aggregation of tau intracellularly by treating the cells with sonicated heparin-assembled recombinant P301S tau fibrils (Figure S1A) in the presence of lipofectamine.